Kenwood ts 480sat wired direct to battery only showing 70/80 watts transmit with engine off,, start engine 100 watts transmit now showing, also have a ft 7900 wired direct to battery, engine off display shows 12.6 volts, engine running 14.6 shows, no probs with the 7900, but cant work out why the power drop with the 480 and engine off, its getting the volts it need according to the manual and if the battery cant supply the 20 amps it needs then I,m pretty sure my jeep wouldn't start, voltage drop in the cable run maybe, but as said the ft 7900 display show 12.6 v, both radios are using 12AWG wire runs and length from radios to battery are approx. 8 ft. anyone got an idea.thanks

It is nothing to get in a twist about as it will never be seen down range. Some rigs like 13.8v for full output. You are loosing 1 volt in feed with 20 amp load. If you up-size to two 12ga wire in parallel for each leg (which is equal to a single 8 ga) the loss will only be .4 volts.

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Most rigs are spec'd to 13.8V +/- 15%. On the low end that would be 11.73V

Your 7900 is reporting 12.6V at "no load" (not transmitting).

16ft of 12ga has .559V of drop at 22A. 12.6-.559=12.041V.

That should still be enough voltage for full output, so something else might be dropping voltage like a connection or a fuseholder. Check the voltage at the back of the radio during transmit to see what you're actually getting.

Don't worry about it, nothing is wrong. If you tried it in the house on a variable PSU you would see the output power drop as you lowered the voltage. My TS480 does the same and my Icom 7000 dropped down to 50W. The difference between 100W and 80W is maybe 1dB, 1/6th of a S point at the other end.

Many times the battery can and does supply sufficient amperage to start the vehicle--even if the battery voltage falls below 12 volts when the car is being started. Chances are that the battery is nearing the end of its useful life. Could be that is why the rig is showing lower transmitter power when the vehicle is off. Check and clean the battery terminals first--that may be all that is needed. But...

I just had that happen to one of my vehicles--sitting the voltage was just above 12 volts, but when I tried starting the car it dropped drastically and the car wouldn't start. Battery terminals were OK. (I disassemble and clean them every three to six months.) I turned on the headlights with the car off and the voltage supplied dropped down to below 11 volts, and continued to drop. Alternator was and is OK, and with a new battery, everything was back to normal.

Are you in an area where it's starting to get colder now? If you are, I would seriously consider replacing that battery because it may give out on you one morning. Good luck and 73!

What you experience is normal for the TS-480 (I have one in the car). You have three choices:

1. Run reduced RF power when the automobile engine is OFF2. Run full RF power when the automobile engine is ON3. Run full RF power when the automobile engine is OFF by using an MJF-4416B Battery Voltage Booster

All you need to do is put the radio on FM , use two needles, one poked into the RED wire and one poked into the BLACK wire right smack where they enter the radio. Take a reading with a DVM BEFORE and AFTER keydown on FM FULL power and tell me what the voltage drop is with out the engine running. 12 gauge is not enough , more like 10 or 8. You want less than 2/10ths of a volt drop between loaded and non loaded conditions.

The vast majority of solid state transceivers will have reduced power out sat voltages. This is true of the 7900 as well.

A good example of this is the Icom V8000. It is factory rated at 13.8 vdc, and an output of 75 watts. The ARRL lab couldn't get more than 73 watts out at 13.8, but could at 14.0. At 12.2, the resting voltage of most lead acid batteries, the output was a scant 47 watts.

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